Nebula is an interstellar cloud of dust, hydrogen, helium and other ionised gasses. The discovery of nebula goes back to the early 1600s. Nicolas-Claude Fabri de Peiresc discovered the Orion Nebula in 1610 using a refracting telescope. Nicolas-Claude Fabri de Peiresc used this telescope to observe the skies, for example, it was used to observe Jupiter’s moons as well as other aspects of space, including nebulae. The discovery of the Orion nebula was revolutionary. While it was Nicolas-Claude Fabri de Peiresc who discovered the Orion nebula, Christiaan Huygens in 1659 was the first person to produce a detailed study on it.
Huygens works led him to discover several interstellar nebulae and some double stars. Nebulae vary vastly in size, some nebula can be found to be millions of light years in diameter. Nebula can also be said to very low in mass. A hypothetical nebula the size of Earth would have a total mass of around 1-4kg. Most nebulae are only visible due to their fluorescence caused by hot stars far within the cloud. Nebula can often be thought to be a star forming regions as well as lead to the formation of planets and any other planetary systems objects.
In the past, any astronomical object was once referred to as nebula, this includes galaxies beyond our solar system and the milky way. Using the Andromeda Galaxy as an example, it was once referred to as the Andromeda Nebula. Other spiral galaxies were referred to as spiral nebulae. Galaxies were confirmed in the early 20th century by many scientists these include, Edwin Powell Hubble and Vesto Slipher. Slipher was an American astronomer who is most known for being the discoverer of galactic red shifts.
The method of spectroscopy was used to monitor the rotation of planets and the composition of planetary atmospheres. By doing this it allowed him to observe the shift of spectral lines of galaxies. Edwin Powell Hubble can be regarded as one of the most important astronomers of all time. What makes him important is that from his work he provided evidence that there is recessional velocity of a galaxy as it increases its distance from Earth, From this Hubble’s law was conceived. Hubble’s law serves as one of the pieces of evidence to support the big bang model.
Hubble’s law is often expressed with the equation v = H0D, where v is the velocity, H0 is the Hubble constant and D is the distance. Hubble’s work with the 100 inch Hooker telescope allowed him to find that some previously discovered nebulae are in fact galaxies beyond the milky way. An example of one of his findings is that the Andromeda nebula was in fact another galaxy, which today is known as the Andromeda galaxy. How Nebula is formed: Due to the vast number of types of nebula, there is a multitude of ways in which nebula is formed.
One place in which nebula is formed is during stellar evolution, specifically in the late stages of it. Stellar evolution is the changes a star goes through over time. As seen in figure 1, all stars life cycles are dependent on their solar masses. It is apparent that the higher the solar mass for the star, the lower its lifetime. Stars, in fact, are initially born in nebula and most create nebula towards the end of their life. An example of stellar evolution we see today can be seen from our sun, a red giant. During the lifecycle of a star, it is powered by nuclear fusion, and the sun has a hydrogen-helium core.
Towards the later stages of a star’s life it begins to drain its nuclear fuel and if it is a red giant like the sun, its core will collapse and will turn into a white dwarf, the outer layers of the sun will be removed as planetary nebula. It can be said when a red giant turns into a white dwarf its temperature increases, this means the amount of ultraviolet radiation emitted increases. This ultraviolet radiation ionises the nebula that was created in the outer layers of the red giant at the end of its life. Another example of a way in which nebula is formed is when there is a gravitation collapse in interstellar space.
Some types of nebula are formed from gasses that are already present in the interstellar medium. The interstellar medium is the matter that exists in space between stars in a galaxy. An example of this is the Carina nebula. The carina nebula is a large molecular cloud. A molecular cloud is a type of interstellar cloud which has a large accumulation of gas, plasma and dust. This accumulation gives the interstellar cloud a greater density than the interstellar medium, this results in the gas, plasma and dust all to clump together, thus resulting into nebula.
Stars can be created from this molecular cloud but only if certain parameters are met. These parameters are; the gravity must overcome the density and force the dust and gas to collapse, This then allows the star formation process to begin. A third way in which nebula is created is as a result from a supernova. A supernova is caused when a star with high solar mass runs out of its nuclear fuel, When it runs out of this fuel it stops generating fusion energy and its core collapses inwards under the force of its own gravity. A supernova can form a neutron star or form a black hole.
Post supernova a supernova remnant is created. A supernova remnant is a structure created from a star exploding during a supernova. This structure consists of ejected material from the star as it approached supernova. When the supernova occurs these materials are swept away and are expelled into space. This is a result of the shockwaves created from the force created by the supernova. These shock waves gather vast amounts of dust which can form into nebulae. An example of nebulae formed from a result of supernova is the crab nebula. The crab nebula as seen in figure 3 is the remnant of supernova 1572.
